Actress Jada Pinkett Smith's hair loss is at the root of the most talked-about moment at Sunday's Oscars ceremony.
Smith disclosed four years ago that she has alopecia and it's the reason she has shaved her head or worn turbans in public.
The autoimmune disease attacks hair follicles.
It's unclear if comedian Chris Rock knew about it when he joked about her baldness during the ceremony.
But his comment prompted a smack and profane admonishment from Smith's husband, actor Will Smith.
The comedian was presenting the award for the best documentary when he made a joke about Pinkett Smith, saying he was looking forward to a sequel to "G.I. Jane" because of her shaved head, the Associated Press reported.
After the joke, Smith got up out of his seat, walked up to Rock, and slapped him.
Once he sat back down, Smith shouted to Rock twice, “keep my wife’s name out of your (expletive) mouth.”
On Monday, the Academy of Motion Picture Arts and Sciences condemned Smith's actions and announced they were launching an investigation.
The National Institutes of Health says alopecia affects all racial groups, men and women equally.
There is no cure.